Here's a proposed design for a little straight-pipe engine that can be made by anyone with a vise, a drill, a rat-tail file and some way to weld on the front end and plug mount.

If you use my favorite 1.25-inch OD antenna mast for this, you should end up with an engine that weighs less than a pound. And who knows? You might even get more thrust than weight out of it, if you're lucky (and if it runs at all, of course ;-)

This is so simple I might even make one myself. It is not really much harder to do than Bruno's 'Simplest Valveless' engine he posted a while back on this forum.

The front edge of the intake slots can be pried out slightly by local heating and gently prying with a screwdriver or chisel point. The rear end flare can also be done easily with local heating.

Since I expect flame to ooze out along the sides, I named it after Henri Coanda, in memory of him and his fabulous Coanda Turbine Plane, which also had flames flowing along its sides.

Comments / criticisms welcome, as always.

L Cottrill

EDIT: Added a couple of needed dimensions to the drawing: the value of the L/8 section, and the width of the mashed section, as seen in the Top View. Sorry about the omissions.

But first, Larry, let me thank you for the analytical effort that went into thinking this whole thing up. If your approach works, it may well be a minor revolution in the field of enthusiasts' valveless pulsejets.

Also, I like this engine for its utter simplicity. I might be built without welding, too.

Now to the disagreement. The point of the Reynst engine is the internal flow in the form of a single big toroidal vortex. Because of such a flow arrangement, a proper Reynst works without a tailpipe.

Other engines have closed ends and all ports on one side, but non of them have this form of internal flow. No other pulsejet I know will work without a tailpipe, either.

The vortex flow might be there in some engines as an accidental feature of the design, without anyone (including the designer) being aware of it. It is a moot point and am not including it into the discussion.

So, Larry, your engine is indeed a kind of an inline Chinese more than the Reynst, precisely because it prevents the Reynst-style vortex flow. I'd wager that it would not work without the tailpipe.

My suggestion would be to forget about the intake slots and propane. Instead, cut a circular hole in the flat side of the squashed part, near the transition to the exhaust part of the duct. Mount a moped carb onto the hole. Some kind of a connecting flange might be necessary.

If it works, and I think it might, it will be the enthusiast's prayer answered. I am really, really envious of the idea. It's such a neat distillation of several threads of thought that have been entertained in this forum. I just wish I did it.

Bruno Ogorelec wrote:Now to the disagreement. The point of the Reynst engine is the internal flow in the form of a single big toroidal vortex. Because of such a flow arrangement, a proper Reynst works without a tailpipe.

Other engines have closed ends and all ports on one side, but non of them have this form of internal flow. No other pulsejet I know will work without a tailpipe, either.

The vortex flow might be there in some engines as an accidental feature of the design, without anyone (including the designer) being aware of it. It is a moot point and am not including it into the discussion.

So, Larry, your engine is indeed a kind of an inline Chinese more than the Reynst, precisely because it prevents the Reynst-style vortex flow. I'd wager that it would not work without the tailpipe.

All right, now. The main problem here is that while you are being semantically exact, I am not - and I have admitted this before! When I say "a Reynst is a Reynst is a Reynst," I am not talking about the details of flow, but rather about the wave mechanics ONLY. My 'Reynstodyne' monicker is applied to any design of mine that exhibits the basic cycle of rear-chamber breathing that was probably first realized by Reynst. They are not meant to be full mechanical equivalents of the famous Reynst Pot, only wave mechanical equivalents.

No, I don't support the Reynst super-vortex in my designs. No, the chamber is not claimed to be able to oscillate on its own. The point is that, once Reynst lowers the stack onto the Pot so they are closely coupled, the acoustic pattern is set for the engine to act as a unit, and it apparently at that point has the same ratios that Bill Hinote observed in later engines like the Chinese and some of the Thermojets. Sure, the vortex is an interesting and even crucial detail, and equips the engine to handle all manner of crudely refined fuels, etc. But it isn't what makes the sucker breathe. It is a 'Reynst breathing engine' because the right lengths are laid out at exactly the right points!

Sure, this is something like an inline Chinese because the Chinese is proportioned for Reynst breathing. So is the SNECMA turbine driver engine; so is the Short Lady; so is the Thermojet. Their individual claims to performance are in the details; but they start and run because the numbers are right - period. My engines won't work without the tailpipe, and neither will the rest of these; but nobody expects them to! They're perfectly usable engines even if they're a metre long - and some of mine don't come close to that size, and they still run!

To me the point is always: It has to be light, it has to be simple to build, it has to be easy to use, and it has to run. Of course, it ought to be compact to the extent that we can get it, and it ought to work with carburetion and non-pressurized liquid fuel well enough for ordinary sport flying. I've started to achieve reasonable compactness [lightness is mostly a matter of better materials] and one or two others are at work on the liquid fuel issue. It's just a matter of time.

I'm still a little confused, Is larry's jar an exception to the rule / not a true reynst?

Well, a jam jar is a 'true Reynst' if there is such a beast. When I say 'Reynst combustor' I usually mean the improved version with the internal central diffuser, though the same swirl pattern can be achieved in other configurations, like the simple jam jar. The point is that the mixture must not enter the chamber and immediately get roiled into a myriad chaotic vortices, but continue to flow. That is the whole point, not what the chamber looks like.

Larry Cottrill wrote:No, I don't support the Reynst super-vortex in my designs. No, the chamber is not claimed to be able to oscillate on its own. The point is that, once Reynst lowers the stack onto the Pot so they are closely coupled, the acoustic pattern is set for the engine to act as a unit, and it apparently at that point has the same ratios that Bill Hinote observed in later engines like the Chinese and some of the Thermojets. Sure, the vortex is an interesting and even crucial detail, and equips the engine to handle all manner of crudely refined fuels, etc. But it isn't what makes the sucker breathe. It is a 'Reynst breathing engine' because the right lengths are laid out at exactly the right points!

Right. I concede the point. And I still love your engine. I hope it works.

The proof is in the pudding. For me, I have toyed with a lot of pipes with holes, and for some reason I have never gotten anything more that a loodle loodle sound/flutter. A length of tubing or side porting will increase the voracity well over a simple hole, at least this is what I have found in my tinkerings. I think feedback develops best with a competing port, one that offers more resistance. Or perhaps the other extreme would work as well, a very Reynst kind of breather, you can't let the air/combustion escape easily, you must match the force to some extent.
Mark

Go back to my second drawing in my 'Secrets of the Dead ...' post. The Henri is just a further simplification of that, but the resonant intake stack is still present.

Of course, we're "debating" something that we don't even know will run ... you could be right and all we'll get is some 'loodling'.

The nice thing about the Henri is that once you have the pipe and other junk in hand, it should only take a couple of hours to do the whole thing. Low cost, too, if it doesn't turn out to be anything after all.

If you imagine the basic valveless pulsejet, say the Schubert with front intake snorkel, imagine keeping the body and disposing of the snorkel. It's hard to see a way to make it run well with just a hole of a size and placement of your choosing.
I think of the failed jam jars I tried with thick lids. It's pretty sad when you can't get a jam jar to run. Maybe a bunch of smaller holes around the perimeter of the Schubert would be worth a try. There's a lot going on with holes. On some level, you could say a snorkel is sensed as a very thick wall by the pulsejet body.
I really don't know where I am going with all this, there are so many variables in those no moving parts engines.
Mark

Mark wrote:On some level, you could say a snorkel is sensed as a very thick wall by the pulsejet body.

Exactly. Inversely, a 'hole' is but a very short pipe. So, plenty of small diameter holes equal a single tubular intake stack. I used to know how to calculate the equivalents, say a single 50-milimeter dia tube 500 mm long equals how many 1-milimeter dia holes in teh wall 1 mm thick. Damn if I know how to do it anymore. I remember it involved the tube diameter, and length, a 'surface roughness constant' for the condition of the tube wall, gas temperature, the pressure differential and something else. (The Reynolds number?) I wish I have not forgotten so many things.

To me, the nice thing about holes is that their air column resonance is very weak, i.e. it would have very high frequency and abominable Q. That would mean that while they might have huge impact on flow, they would have very little effect of their own on the gross wave mechanics of the engine. Is this a reasonable appraisal?

If it is, the logical form of a hole for carburetion would be a very short venturi. In fact, it might be logical to make a 'bullet venturi', like a hole with a small steel ball in the middle of it that the air has to accelerate around to get through. I can imagine a jam jar with a two-washer 'hole' with fuel creeping through it [as has already been tried by Eric, Steve and maybe others] with a streamlined bullet in the middle. High velocity for good suction, and plenty of fuel-laden perimeter for feeding.

Something like that might be a nice bit for fueling the 'Henri' engine from one side, sort of what Bruno was talking about by attaching a regular carburetor but much lighter and simpler [maybe].

Well, I got to mess with this for about an hour tonight and got the pipe cut and pinched and properly marked up for drilling & filing the intake slots. The .87 inch dimension for the pinch shown on the drawing is way off - I stopped at .75 inch and that actually looks about right.

Doesn't sound like much accomplished in an hour, but of course I was taking construction photos as I went along. I think it looks even more promising in real life than in the drawing.

You know, Ive just realized that we are really making a kind of a revolution -- and you are among its most prominent figures. A Che Guevara of pulsating combustion.

(Keep up the poster work. Judging by how the image of Che did as a commercial item, there's millions in this business.)

What I'm trying to say is that what we're doing here is ground-breaking. We are distilling jet propulsion to its barest possible essentials.

This is philosophically different from what Tenney and Marks were doing with the Dyna-jet. They were trying to make a big jet engine small. (They did an absolutely brilliant job, mind you; I'm not trying to diminish their achievement, just analyzing the respective approaches.)

What we are really trying to do is to pin down the character of the beast in order to reduce it to its barest essentials -- and then make it possible for people to build a jet engine at a drop of a hat. This is quite amazing really -- we are bringing jet propulsion down to the level simpler than some ambitious school projects.

Please don't forget Maggie Muggs, either. Not because a ramjet is ever going to be a practical engine for an enthusiast, but because it uses off-the shelf components.